I am using ktorrent 2.2.7 and have noticed that when seeding and a leecher running Transmission connects, the 'uploaded' on the peer display continues to increase well past the size of the torrent but the availability% only increases very slowly (eg currently a Transmission client is leeching a 49MByte torrent and the peer display shows that I have uploaded 70MByte to that peer but the peer's availability only shows 16.50%). This only seems to happen when the leecher is running Transmission. Is this a problem with ktorrent or with Transmission?

Probably transmission, because the leeching clients need to update one another on how many pieces they have downloaded.

Could be that the transmission client is having trouble with some bad peers who are corrupting it's downloads.